Re: inheritance, list of objects, polymorphism

  * Make sure that objects can only be created dynamically.
    The reasonable way is to make the destructor protected.

  * Force use of smart pointer.
    James relies on garbage collection so he probably doesn't do
    this, but there are two aspects: ensuring that any newly created
    object's raw pointer is immediately stored in a smart pointer,
    and ensuring that only the smart pointer class has access to
    destroy an object. One way to do the first it is to overload
    the class' allocation function (operator new) so that any direct
    'new' expression would be overly complicated. For C++98 then
    provide a macro that supplies the requisite magic
    incomprehensible expression and ensures the pointer is
    immediately wrapped in a smart pointer, before client code can
    get at it. For C++0x I think the improved support for argument
    forwarding makes the macro unnecessary. Anyways, one way to do
    the second is to make destructor protected (which you'd do
    anyway for the bullet point above), and grant friendship to the
    smart pointer.